Sewing a gas bag is one of the most labor-intensive and thus most expensive manufacturing steps in the production of a gas bag. Primarily with gas bags that obtain their three-dimensional shape in the inflated shape by the fact that their outer envelope does not only consist of two strips flatly sewn on top of each other, there is often the necessity to close seams for which the blank parts cannot be spread on a table completely flatly. This kind of fabrication is, of course, laborious and expensive. It is, therefore, endeavored to create gas bag blanks also for three-dimensional gas bags in which all of the seaming processes may be carried out with so-called “two-dimensional seams”, with the blank parts lying flatly on a base.